VMware is claiming it doesn't need to deliver on its promise of a bare-metal desktop hypervisor, but says that if it does choose to release a so-called Type 1 client hypervisor it would be better than Citrix's.

"Let's set the record straight there," says Vittorio Viarengo, vice president of desktop marketing for VMware. "If there's one company that can nail a client hypervisor, it's VMware."

VMware certainly believed that statement when it said it would deliver a bare-metal desktop hypervisor by the end of 2009. But more recently VMware executives have said building such a technology "is not an easy computer science problem to solve," and that it is no longer making any promises on when VMware's bare-metal development would turn into a marketable product.

At VMworld in San Francisco this week, VMware will release version 4.5 of VMware View, its desktop virtualization platform, but it won't include a bare-metal option.

Citrix has beaten VMware to the punch here with its own XenClient, while startups Virtual Computer and Neocleus have been shipping products for some time.

Another company, MokaFive, says it will have a bare-metal hypervisor on the market early in 2011.

But VMware now says customers aren't ready for a bare-metal hypervisor. VMware's project is in its advanced development labs and could be ready fairly quickly once the company decides to turn it into a product, Viarengo says. But it's not VMware's top priority.

"Just from a priority perspective, it took a back seat for now," Viarengo says.

Bare-metal desktop hypervisors install directly onto a computer's hardware, rather than on top of a host operating system as Type 2 hypervisors do. Analysts and some vendors believe this will provide greater isolation between virtual machines, therefore improving security and making it more feasible for IT to install corporate operating systems and applications onto employee-owned machines.

But bare-metal is still in the early stages of development, and not just at VMware.

Today's bare-metal client hypervisors are "not robust at all," and more of a "niche technology," IDC system and virtualization analyst Ian Song said in a recent interview.

While installing a Type 2 hypervisor on top of an operating system is relatively easy, the hardware on today's PCs would in many cases not be compatible with a Type 1 hypervisor, says Scott Davis, CTO of VMware's desktop business unit. The goal of letting users access corporate applications on personal machines is best met by Type 2 technology, at least for now, he says. Today's Type 2 hypervisors do a better job ensuring that corporate OS images can run on the same machine as personal desktop images without causing security risks, he says.

"We decided from a priority perspective that there are ways to solve a wider range of use cases with a Type 2 approach," Viarengo says.But just as Type 1, bare-metal hypervisors replaced Type 2 technology on servers in the data center, bare-metal virtualization is likely to play a role in the future of desktop technology. VMware is unlikely to scrap its bare-metal plans entirely, but is at risk of falling behind the competition by waiting.

Citrix's XenClient could start shipping on PCs sold by hardware vendors as early as the first quarter of next year, Burton Group analyst Chris Wolf has said, adding that "If VMware doesn't even have a product in beta by that point, you would have to say VMware is at least a year behind."

VMware's public statements indicate the company believes it's not risking much by not having a bare-metal hypervisor ahead of rival Citrix. Remarks by Viarengo and Davis are similar to ones made by VMware CEO Paul Maritz in July when the company reported its financial results.

"We are providing client-side -- big client-side -- functionality with our offline View capability, which comes as part of [VMware View] 4.5," Maritz said, as quoted by The Register. "The feedback that we got from our customers is the market is not ready yet for a bare-metal, naked hypervisor. So instead we are supplying essentially a Windows-within-Windows hypervisor, which gives us much better coverage over the installed base in particular. The challenge with the bare-metal hypervisor is: 'how do you address the installed base?' So we made that change based on customer feedback."